What Is an Implantable Defibrillator?
A defibrillator is part of a defibrillation system that has three main parts: the defibrillator, leads, and a programmer. Two parts of this system are placed inside the body.
The defibrillator is a small metal case that contains electronics and a battery. It is similar to a pacemaker in that it is designed to correct arrhythmias. But while a pacemaker increases a slow heart rate, a defibrillator detects and corrects fast and slow heart rates.
Leads are specialized, thin, insulated wires that are attached to the defibrillator. Leads sense the heart's rhythm and deliver therapy to the heart (as directed by the defibrillator).
The third part, the programmer, is kept in a hospital or clinic. A doctor or nurse uses this specialized computer to monitor and change the instructions of the implanted defibrillator.
The three parts of the system work together to detect the type of fast heart rhythm (tachyarrhythmia) and then treat the heart until a more normal rhythm results. Some defibrillation systems can also detect and treat a slow heart rhythm (bradycardia).
Different therapies are used to reset the heart rhythm back to normal. However, a defibrillation system does not cure or prevent the arrhythmia. Instead, the system stops the arrhythmia and stores information for the doctor to evaluate later.
Part 1: Defibrillator
An implanted defibrillator is a small automatic device that detects and treats fast heart rhythms (tachyarrhythmias). Some defibrillators can also treat a slow heart rhythm (bradyarrhythmia), which can occur along with tachyarrhythmias.
The titanium metal outer case encloses a battery and a microprocessor. On top of the metal case is transparent plastic that connects a lead to the defibrillator.
Battery. The defibrillator battery supplies the electrical energy for the therapies that are delivered. How long this battery lasts depends upon the kind of therapy delivered and how often therapy is delivered. (When the battery needs replacing, the entiredefibrillator is replaced.)
Microprocessor and Circuitry. The microprocessor is like a very small computer. When an arrhythmia is detected, a therapy is delivered to return the heart to a more normal rhythm.
The defibrillator has an electronic memory that stores important information: the number and types of treatments you receive, how successful each treatment was in stopping your rapid rhythm, what your heart was doing during your most recent episodes, and the status of the defibrillator’s battery and programmed settings. This information is retrieved by the doctor or nurse at a follow-up visit.
Part 2: Lead
A lead is a special insulated wire that is connected to an implanteddefibrillator. Leads are extremely flexible in order to withstand the twisting and bending caused by body movement and movement by the heart itself.
A lead performs two functions:
It carries electrical energy from the defibrillator to the heart.
It relays information about the heart's electrical activity back to the defibrillator.
Where a lead is placed: inside or outside of the heart. A lead may be inserted through a vein and placed inside the heart. This is called an endocardial lead ("endo" means inside) or a transvenous lead (because it is inserted through a vein).
When a lead is attached to the outside of the heart, it is called an epicardial lead ("epi" means outside). An epicardial lead is often used when another surgery is being done and the outside of the heart is easy to reach.
Medication where lead touches the heart tissue. The location where the lead touches the heart naturally produces an inflammatory response. This response is similar to what is observed when you've scraped your skin: the area around the scrape is red and may result in a scar as your body repairs itself. When a lead is placed in your heart, a similar response occurs. Placing a medication at the tip of the lead reduces this inflammation.
The special medication placed at the tip is called a steroid. This very tiny amount of steroid (less than 1 mg) is located just at the tip of the electrode. When the lead is placed in (or on) the heart, the medication is released and the build-up of scar tissue between the electrode and the heart tissue is minimized. Reducing the amount of scar tissue helps the pacing system work more efficiently.
One or more leads are used, depending on your medical condition
Part 3: Programmer
A programmer is a specialized computer used to monitor and adjust pacemakers or implantable defibrillators.
During a follow-up visit, or during a hospital stay, a doctor or nurse may place the magnetic wand (or programming head) of the programmer over the implanted device. This allows the programmer to:
receive information from your device (pacemaker or defibrillator). The information received from the device shows how your device and your heart have been working. Based on this information, the doctor or nurse may want to change the therapy.
send instructions to your device. When the therapy needs to change, the nurse or doctor can send the new instructions to the implanted device – without any surgery.
A programmer is one part of a defibrillation system which helps your heart condition. The system is a combination of a programmer, a defibrillator, and cardiac leads working together.
Follow-up visits are important to ensure that the implanted defibrillator continues to provide the best treatment for your arrhythmia. The purpose of these visits is to:
Assess your medical condition and find out about any lifestyle changes
Check the defibrillator's battery status and its programmed instructions for delivering therapy
Monitor any medications that are taken
Provide psychological support
The frequency of follow-up visits is determined by your doctor. It is common to have a first follow-up visit one month after receiving a defibrillator. Depending upon your doctor's usual practice and your medical condition, later visits are scheduled every three to six months.
During the visit, the doctor or nurse will use the programmer to retrieve stored information from your device. If your medical condition changes, the doctor may reprogram your defibrillator to better treat a rapid rhythm. No surgery is required at follow-up visits. The visits typically do not take longer than a regular doctor's appointment.